This invention relates to tone control circuits.
Conventionally, a negative feedback type tone control circuit, a capacitance-resistance (CR) attenuation type tone control circuit and a CR-negative feedback type tone control circuit, has been available for boosting or cutting high-pass or low-pass in a sound system in order to control tone. A known negative feedback tone control circuit as shown in FIG. 1 is comprised of an inverting amplifier 1, resistors 2, 3, 4 and 5, capacitors 6, 7 and 8 and variable resistors 9 and 10. Low-pass boosting or cutting is controlled by variable resistor 9 and high-pass boosting or cutting by variable resistor 10. Shortcomings exist in this circuit such as (a) the phase between the input and output inverts and (b) due to the low input impedance and presence of a frequency characteristic, a buffer amplifier with low output impedance is always required at the previous stage.
A known CR-attenuation type tone control circuit as shown in FIG. 2 is comprised of resistors 11, 12, 13, 14, 15 and 16, capacitors 17, 18, 19 and 20, and variable resistors 21 and 22. Low-pass boosting or cutting is controlled by variable resistor 21 and high pass boosting or cutting by variable resistor 22. Shortcomings exist in this circuit such as (a) the insertion loss is extremely large, (b) due to the low input impedance and presence of a frequency characteristic, a buffer amplifier with a low output impedance is always required at the previous stage, (c) variable resistors 21 and 22 must be A-type variable resistors which have a complex rotation angle to resistance variability characteristic and thus have poor precision and produce greater errors thereby causing waviness in the flat area of the tone control characteristics, (d) frequent interference between the low-pass side circuits and the high-pass side circuits makes designing extremely difficult, and (e) when variable resistors having identical rotation angle to resistance variability characteristics are used for the high-pass and low-pass variable resistors, the ratios of boosting and cutting variations to the rotation angles of the sliders of the variable resistors are different between the treble and the bass as shown in FIGS. 4(a), (b) and (c) where FIG. 4(a) shows tone control characteristics, FIG. 4(b) shows the rotation angle of the slider of the low-pass variable resistor and FIG. 4(c) shows the rotation angle of the slider of the high-pass variable resistor. Common numerals are used in FIGS. 4(a), (b) and (c).
The known CR-negative feedback tone control, circuit, as shown in FIG. 3, is a CR-attenuation type tone control circuit inserted into the negative feedback loop of the inverting amplifier. It is comprised of an inverting amplifier 1, resistors 23, 24, 25, 26 and 27, capacitors 28, 29, 30 and 31 and variable resistors 32 and 33. The high-pass boosting and cutting and low-pass boosting and cutting are effected respectively by controlling variable resistors 32 and 33. Shortcomings exist in this circuit such as (a) contrary to the CR-attenuation type tone control circuit, it has a gain, (b) the variable resistors must be C-type variable resistors with complex rotation angle to resistance variability characteristics, which have poor precision and produce greater errors, thereby causing waviness in the flat area of the tone control characteristics, (c) frequent interference between the low-pass side circuits and the high-pass side circuits makes designing extremely difficult, (d) when variable resistors having identical rotation angle to resistance variability characteristics are used for the high-pass and low-pass variable resistors, the ratios of boosting and cutting variations to the rotation angles of the sliders of the variable resistors are different between the treble and the bass as shown in FIGS. 4(a), (b) and (c).
In particular, the shortcoming (e) in the CR-attenuation type tone control circuit, which is the shortcoming (d) in the CR-negative feedback type tone control circuit, is an important shortcoming, it being attributable to the interference of the bass side circuits on the treble side circuits. In order to eliminate this shortcoming, variable resistors with different resistance variability characteristics to rotation angle of the variable resistor must be used as the high-pass side and low-pass side variable resistors. Thus, it has a shortcoming of requiring variable resistors with markedly complex characteristics.
It is thus a primary object of this invention to provide an improved tone control circuit that eliminates the above shortcomings, particularly a tone control circuit that has less interference between the treble side circuits and the bass side circuits and one that can equalize the boosting and cutting variation ratios for the treble and the bass by using variable resistors with a linear rotation angle to resistance variability characteristics.
Other objects and advantages of this invention will be apparent from a reading of the following specification and claims taken with the drawing.